Radio receiving system



Examint Sept. 28, 1937. v. D. LANDON RADIO RECEIVING SYSTEM Filed Nov. 14, 1928 INVENTOR l/ernonDLandon.

ATTIORNEY Patented Sept. 28, .1937

UNITED STATES Examiner PATENT OFFICE RADIO RECEIVING SYSTEM Vernon D. Landon, East Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application November 14, 1928, Serial No. 319,234

11 Claims.

My invention relates to radio receiving systems and apparatus, and it has particular relation to systems wherein signals received upon a single energy receptor are distributed to a plurality of indicating devices.

5 various apartments, but the number and variety of programs thus available to the tenants through such a system is obviously limited. Furthermore, the initial cost of an audio-frequency distribution system, if more than one or two separate programs are to be made available, is high, and a skilled attendant must be kept always available to supervise the tuning of the receiving apparatus and to adjust the amplifiers feeding the distribution network.

It is, accordingly, an object of my invention to provide a distributing system whereby an unlimited number of radio programs may be made simultaneously available in any one of a pinrality of rooms of a building.

Another object of my invention is to provide a distributing system of the type described wherein the programs are simultaneously transmitted to the several rooms by means of radio-frequency currents.

Another object of my invention is to provide, in a radio-frequency program-distributing system, means for preventing interaction, and consequent' interference, between the individual receiving sets coupled to the distribution network.

Another object of my invention is to provide, in a radio-frequency program-distributing system, means for preventing any one of the individual receiving sets coupled to the distributing network from adversely influencing the reception of signals by any of the other receiving sets.

Another object of my invention is to provide a system of the type described through the use of which programs may be distributed by means of radio-frequency currents without detrimental T attenuation.

Another object of my invention is to provide, in a system of the type described, means for preventing local extraneous disturbances from interfering with the reception of signals.

Another, and more specific object of my invention is to provide, in a system of the type described, means whereby the elements constituting the distribution network for radio-frequencies may be utilized for conveying direct current from the central station to the locations where individual radio receiving sets are installed.

In the particular embodiment of my invention shown in the drawing, I provide a single energy receptor, or antenna that is rendered aperiodic by the inclusion therein of a high resistance device. A plurality of amplifier tubes are so disposed with reference to the resistance device that a portion thereof constitutes the input circuit of each tube, the number of tubes being chosen to equal the number of the wings, or sections, of a building that are to be supplied with signalenergy at radio-frequencies.

The output circuit of each of the amplifier tubes, which will hereinafter be referred to as antenna-coupling tubes, comprises the primary winding of a step-down transformer, the secondary of which constitutes the input impedance of a double-conductor transmission line. The midpoint of the secondary winding is connected to ground through a resistor. The midpoint of a terminal impedance device which is connected across the far ends of the transmission line is also grounded through a resistor and a condenser.

Each transmission line is enclosed in aconductively-grounded metallic conduit thereby preventing the line from picking up stray disturbances, caused by sparking elevator-control contacts, etc., the conduit being also utilized for the transmission of plate-potential from a central station throughout the building.

At each point where the transmission line is to be provided with a branch connection, or where the high-frequency signals are to be demodulated and rendered audible, an individual coupling tube is provided, the input circuit of each tube being connected between one of the conductors constituting the transmission line and the grounded conduit.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and the theory upon which it is based, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing:

The single figure of the drawing is 9. diagrammatic view of a portion of a radio-frequency signal-distributing system comprising a preferred embodiment of my invention.

antenna 5, a condenser 2, a high resistance device 3 and a ground connection]. The condenser and resistor are preferably enclosed in a metallic container '5 that, for best results, is disposed closely adjacent to the antenna, on'the roof of a building. a a

A' grounded metallic container is disposed closely adjacent to the container 5, and in it are mounted an antenna-'coupling-tube I; a filamentsupply transformer '8 and a radio-frequency transformer l0. Aresistor II is connected across the filament terminals of the coupling-tube, the central point on the resistor being connected to the metallic container through a large condenser II.

The grid of the coupling-tube is connected to the antenna resistor by a conductor l3, a coupling condenser ll being interposed in the connection. The tube is provided with a grid-leak resistor l5, as is customary.

The central point on the filament-shunting resistor II is connected through a second resistor l6 and a conductor IT to the negative terminal of a source I! of high potential. The high-potential source l8, which may be a B-eliminator of any well-known type, or which may be a battery, if desirable, is preferably enclosed in a grounded metallic container 26, to which the positive terminal of the source is connected.

The plate of the coupling-tube is connected to ground through the primary winding of the radiofrequency transformer Ill. The midpoint of the secondary winding of the transformer I0 is connected to ground over a path including a resistor 2|, a conductor 22, the resistor I8, and the condenser that serves to connect the midpoint of the filament-shunting resistor II to ground.

The secondary winding of the transformer I0 constitutes the input-impedance of a transmission line comprising a plurality of conductors 23 and 24. The conductors may be the usual twisted fiex", the inter-conductor capacity of which is definite and does not change appreciably over a given length.

The transmission line is divided into a plurality of sections, and in each section a loading inductor 25 is inserted in each side of the line. The length of a section is determined by the capacity between the two sides of the line in that section. The capacity between the conductors of the line in any given section should be, for best results at the radio-frequencies now used for broadcasting, of the order of 400 micro-microfarads.

The transmission line terminates in a fixed resistor 26 preferably mounted in a grounded metallic container 21. The midpoint of the resistor is connected to the container through a resistor 28 and a condenser 30.

The transmission line is preferably supported within, and insulated from, a metallic conduit 3|. A plurality of branch conduits 32 are connected to the main conduit 3|, each branch conduit extending to a location where an individual receiving set is to be installed, at which location a grounded, metallic, apartment-coupling-tubecontainer 33 is positioned.

A coupling-tube 34 is mounted within the container 33. The output circuit of the tube includes the primary winding of a radio-frequency transformer 36, similar to the transformer l0, supported within the container. The filament of the tube is supplied with current from the secondary winding of a filament-heating transformer 31 which is mounted within the couplingtube container. A switch is preferably in- I cluded in the connection between the primary 5 winding of the transformer and a source of pcftential therefor, the switch being disposed ex teriorly of the container in order that the coupling tube 34 may be energized at will.

The secondary winding, of the radio-frequency 10 transformer 36 connects to two terminals 40 and U, disposed exteriorly of the container',' from I which terminals leads maybe taken to the antenna and ground binding posts of a suitable radio set, preferably of the type having a resistive input 15 circuit of about 2000 ohms. if

One side of the transmission line 23-44 is connected to the grid of the apartment-coupling tube by means of a conductor 42, the conduit 3| being connected to the filament of the tube over a path which includes a conductor 43, a large condenser 44, and a resistor 45 disposed in shunt to the filament terminals.

The grid of the tube 34 is connected to the filament thereof over a grid-leak path includ- 25 ing an inductor 46 and a resistor 41. Plate potential for the tube is supplied from the source 98 over the conduit 3| and the conductor 43 that connects the plate to the conduit, the platereturn path comprising the filament shunting resistor 45, the grid-leak resistor 41, inductor 4G, and the wire 24 of the transmission line to which the grid is connected.

The radio-frequency transformer mounted in the antenna-coupling-tube box is of the step- 3U down type in order that the impedance of the transmission line may be given a low value for reasons which will later be given in more detail. The transformer mounted in the apartment-coupling-tube box is also of the step-down type.

As many antenna-coupling-tube boxes as are necessary to properly distribute the signals may be associated with the high resistor included in the antenna circuit. Inasmuch as each antenna-" -s nduc ivit ,no mte 45 erence results between the several distribution lines.

In order that the drawing shall not be too complicated, I have illustrated only two-antenna ccuplingube boxes, but this is not to be construed as limiting the number of such boxes that may be employed. It will be noted from an inspection of the drawing, however, that a separate plate-potential source should be provided for each antenna-coupling tube box and the individual 65 apartment-coupling tube boxes associated with the transmission line energized thereby. Such an arrangement is not expensive, inasmuch as each of the plate-supply units may take the form of a B-battery eliminator of simple design.

In order that the operation of a signal-distributing system constructed and arranged according to my invention shall be fully understood, it is considered best to digress somewhat at this point and to briefly outline the theory upon which my 65 invention is based.

The design is based to some extent on the principle underlying a low-pass filter or loaded transmission line. The formulas applying to this circuit are:

(2) {rm/Z5 Examinei where fc is the cutoff frequency, and HT is the terminal resistance. Higher frequencies than the cut-off frequency are attenuated to a degree which increases rapidly as the frequency is increased. Lower frequencies are transmitted with practically no loss.

If E volts are applied at a frequency lower than fc in series with an initial resistor R'r (commonly called the generator resistance) then volts will appear across the terminal resistor R'r providing the circuit is so balanced that Equations (1) and (2) are fulfilled.

These same formulae apply to a groundedneutral circuit, such as that shown in the drawing, when the inductance used for L is that of the two loading coils of one section of the line in series, and the capacitance used for C is the capacitance of one side of the line to the other side, for a single section between loading coils. The distributed inductance of the wires is negligible in this case as telephone twisted-pair wires are used and there is very little space between wires.

We, therefore, must solve a pair of simultaneous equations with four unknowns. Clearly, arbitrary values may be assigned to any two of the variables and the corresponding values of the other two variables may then be determined by the two equations.

The most important factor is fe. A convenient value, for arithmetical simplicity and for practical reasons for c, is 1,570,000, or

cycles. Substituting this value in Equation 2 1o Solving this equation,

or LC=4 10 If a convenient value is next assigned to either L, C, or R, the other two values will then be determined by the above equations.

It is most'convenient to have the loading-coils spaced a distance apart equal to a multiple of the distance between the floors in the building in which the system is installed since the coils may then be placed in the coupling-tube boxes and special boxes need not be provided. If the floors are approximately 10 feet apart, a loading-coil spacing of 20 to 22 feet is desirable. This length of #18, telephone, twisted-pair line has an interwire capacity of a little over 300 mmfd. Allowing about 50 mmfd. apiece for two coupling-tubes (the average number per section of line) gives a line capacity of 400 mmfd. per section. Substi tuting this value in the equation LC=4 10 we have 4.10 4oo 1o" or 100 microhenries. R:- is then fixed, by the equation Z r= at 500 ohms.

A hundred feet of this line is found to transmit signals over the entire broadcast band with a negligible amount of attenuation. The length of each section of the line is not critical. It may be varied 25% with no bad effects.

It now remains to design a suitable transformer to match the plate impedance of the tube (10,000 ohms) to the 500 ohm line load. This requires a stepdown ratio of /20 or about 4.5 to 1. Since it is impractical to build a transformer that is 100% coupled, the leakage reactance thereof appears as the loading inductance of the first section of the line. The inductance of the primary must be great enough to make an effective transformation at the lowest frequency of the band.

Two mlllihenries is found sufilcient for the primary. That portion of the secondary which may be considered 100% coupled to the primary must accordingly have an inductance of or 100 microhenries. Adding to this the leakage reactance of 100 microhenries gives a transformer with a 2000 microhenry primary winding, a 200 microhenry secondary winding, 50% coupling, and an eflfective ratio of 4.5 to 1.

It should be noted that the tube plate-filament capacity, (10 mmfd. usually), multiplied by the square of the tums-ratio, (i. e., 20) supplies the correct terminal capacity for the low-pass filter, 200 mmfd.

The design of the output transformer of the apartment coupling tube is obtained by following a similar line of reasoning. Its ratio is about 2.25 to 1. This matches the tube impedance with an impedance of 2000 ohms, which seems to be a good average value for the input impedance of receivers of various types.

If one volt of radio-frequency voltage is applied on the grid of the antenna-coupling tube, and the amplification factor of the tube is 9, we have volt applied to the grids of the apartmentcoupling tubes, assuming no attenuation. If the input impedance of the radio receiver is 2000 ohms, in order to provide an impedance matching the impedance of the apartment-coupling tube as seen from the transformer, volt applied to the grid of the said tube will develop 1 volt across the input circuit of the receiver. If the impedance of the receiver is other than 2000 ohms the input voltage may be greater or smaller but operation is fairly satisfactory. To make the impedance of the transformer 36 more nearly like that of an antenna, a small condenser 50 may be serially included between the secondary windings thereof and the terminals 40 and 4|.

Thus, the system provides signals at each receiver outlet plug that will be the equivalent of those which would be obtained if the receiver were located on the roof of the building and were the only one supplied from the antenna.

It will thus be seen that I have provided a radio-frequency signal-distribution system whereby a single energy-collecting device may be utilized to provide a plurality of remotely-situated radio receiving sets with an unlimited number of programs distributed by radio-frequency current, each program being selectable by the individual sets at the option of the operator without influencing the reception of other programs by the remaining sets. In addition, proportioning the electrical constants of the individual transmission lines according to my invention, each line is given the characteristics of a bandpass filter which transmits with substantially equal efiiciency all of the radio-frequencies lying within the range for which the system is designed.

Another important advantage of my invention lies in the fact that the shielded transmission lines do not pick up electrical disturbances originating in sparking at elevator-control contacts, and similar interfering impulses. In fact, a radio set coupled to the distribution system is actually quieter in operation than a similar set coupled directly to an antenna of the usual type, since the pick-up that would be present with an unshielded down-lead is eliminated by the shielding.

Inasmuch as many modifications of the specific apparatus chosen for illustrative purposes will be apparent to those skilled in the art, my invention is not to be construed as restricted thereto, but is to be limited only by the prior art and by the spirit of the appended claims.

The manner in which plate-potential for the individual apartment-coupling tubes is transmitted from a central source, in accordance with my invention, is also considered an important feature of the system since the said coupling tubes may thus be kept supplied with potential, without attention on the part of the tenant of the apartment.

I claim as my invention:

1. In a signal receiving and distributing system, means for amplifying signals at radio-frequencies, a transmission line having the characteristics of an electrical filter for conveying said signals to a plurality of remote points, additional amplifying means associated with said line at said remote points, and means for utilizing said line for the transmission of direct currents to said amplifying means. a

2. In a signal-distributing system, a transmission circuit including a plurality of sections having inductance and capacity, a thermionic device, and means for so associating said thermionic device with said line that the plate-filament capacity of said device furnishes the capacity for the initial section of the line, said means also providing the inductance for said initial section.

3. In a system for the distribution of radio programs in an apartment house, a transmission line including a plurality of sections having loading inductance, a thermionic device, and a transformer interposed between said device and said line, the leakage reactance of the secondary winding of said transformer being substantially equal to the said loading inductance.

4. A multiplex high frequency receiving system for operating a plurality of receiving devices from the same energy pickup device, comprising, in combination, means for picking up high frequency energy to be received, a line conductor associated with said pickup for transmitting energy to all of said receiving devices, said receiving devices being connected through an impedance to said conductor at intervals, and loading coils interposed in said conductor intermediate said receiving devices, said line conductor being grounded at its end through a resistance of such value as to substantially prevent the production of standing waves on said line.

5. A multiplex high frequency receiving system foroperating a plurality of receivers from the same energy pickup device, comprising, in combination, means for picking up high frequency energy to be received, a transmission line associated with said pickup means, said line being positioned within an enclosing conductor through at least a portion of its length and being loaded at predetermined points to act as a uniform attenuation line passing energy of frequencies up to the highest desired frequency, and a plu rality of receivers coupled to said line at points electrically intermediate to said loaded points.

6. A multiplex high frequency receiving system for operating a plurality of receiving devices from the same energy pickup device, comprising, in combination, means for picking up high frequency energy to be received, a line conductor associated with said pickup for transmitting energy to all of said receiving devices, said line conductor being surrounded by a metallic conductor through at least a portion of its length, said receiving devices being connected to said conductor at intervals, and loading coils interposed in said conductor intermediate said receiving devices, said line conductor being grounded at its end through an impedance of such value as to substantially prevent the production of standing waves on said line.

7. A multiplex high frequency receiving system for operating a plurality of receiving devices from the same energy pickup device, comprising, in combination, means for picking up high frequency energy to be received, a line conductor associated with said pickup and leading to said receiving devices, means for connecting said receiving devices to said line in energy absorbing relation, said line conductor being enclosed throughout a portion of its length within a conducting casing, and loading coils interposed in said conductor intermediate said receiving devices, the structure of said system being such that said line conductor has an electrically infinite effective length, and the constants of said loading coils having a value such that said line exhibits the characteristic of a uniform attenuation line passing currents of a frequency as high as the highest frequency desired to be received.

8. A multiplex radio receiving system comprising an antenna mounted in position to pick up energy to be received, a line conductor serving a plurality of receivers, means for connecting a plurality of said receivers to said line in energy absorbing relation, loading coils interposed in said line between adjacent receivers to cause said line to have the characteristics of a uniform attenuation line passing all frequencies desired to be received, means for preventing terminal reflection on said line, and said line conductor being enclosed within a grounded metallic conduit.

9. A radio receiving system for protecting a receiver from local interference comprising, in combination, an antenna for collecting signal energy to be supplied to a receiver, a lead-in, a radio receiver operatively associated with said lead-in, a grounded conductor enclosing said lead-in for a substantial portion of its length and insulated therefrom, and maintained at ground potential, and a transformer interposed between the head of said lead-in and said antenna.

10. In a radio receiving system for protecting a receiver from local interference, in combination, an antenna for collecting signal energy to be supplied to a receiver, a lead-in, a radio receiver operatively associated with said lead-in, and a transformer interposed between the head of said lead-in and said antenna, said transformer Examiner and said lead-in being enclosed within a conducting container maintained at ground potential.

11. In a radio receiving system for protecting a receiver from local interference, in combination, an antenna for collecting signal energy to be supplied to a receiver, a lead-in, said lead-in being enclosed within a grounded conducting container, a. radio receiver, means for connecting said radio receiver to said lead-in in operative relation, and means interposed between said antenna and said lead-in for maintaining a uniform energy transfer relation between said antenna and said lead-in over a relatively wide band of 5 frequencies.

VERNON D. LANDON. 

